Poly(1,4-cyclohexylenedimethylene terephthalate) (PCT), a polyester based solely on terephthalic acid and 1,4-cyclohexanedimethanol, is known in the art and is commercially available. This polyester crystallizes rapidly upon cooling from the melt, making it very difficult to form amorphous articles by methods known in the art such as extrusion, injection molding, and the like. In order to slow down the crystallization rate of PCT, copolyesters can be prepared containing additional dicarboxylic acids or glycols such as isophthalic acid or ethylene glycol. These ethylene glycol- or isophthalic acid-modified PCTs are also known in the art and are commercially available.
One common copolyester used to produce films, sheeting, and molded articles is made from terephthalic acid, 1,4-cyclohexanedimethanol, and ethylene glycol. While these copolyesters are useful in many end-use applications, they exhibit deficiencies in properties such as glass transition temperature and impact strength when sufficient modifying ethylene glycol is included in the formulation to provide for long crystallization half-times. For example, copolyesters made from terephthalic acid, 1,4-cyclohexanedimethanol, and ethylene glycol with sufficiently long crystallization half-times to provide for amorphous products exhibiting higher ductile-to-brittle transition temperatures and lower glass transition temperatures than the compositions revealed herein.
The polycarbonate of 4,4′-isopropylidenediphenol (bisphenol A polycarbonate) has been used as an alternative for polyesters known in the art and is a well known engineering molding plastic. Bisphenol A polycarbonate is a clear, high-performance plastic having good physical properties such as dimensional stability, high heat resistance, and good impact strength. Although bisphenol-A polycarbonate has many good physical properties, its relatively high melt viscosity leads to poor melt processability and the polycarbonate exhibits poor chemical resistance. It is also difficult to thermoform.
Polymers containing 2,2,4,4-tetramethyl-1,3-cyclobutanediol have also been generally described in the art. Generally, however, these polymers exhibit high inherent viscosities, high melt viscosities and/or high Tgs (glass transition temperatures) such that the equipment used in industry is insufficient to manufacture or post polymerization process these materials.
Thus, there is a need in the art for sheets and films which may be thermoformed without the need to pre-dry the sheets and/or films prior to thermoforming. These sheets and/or films comprise at least one polymer having a combination of two or more properties chosen from at least one of the following: toughness and moderate glass transition temperature, hydrolytic stability, chemical resistance, good impact strength, long crystallization half-times, low ductile to brittle temperatures, good color and clarity, lower density and/or thermoformability of films and/or sheets comprising the polyester compositions useful in the invention), while retaining processability on the standard equipment used in the industry.